1. Field of the Invention
This invention relates to a method of an emboss pattern process, emboss pattern processing apparatus, and an embossed sheet, which is used for the production of an optical precision embossed sheet, such as a reflector, a prism sheet, a fresnel lens and so on.
2. Description of the Related Art
In recent years, a reflective ability sheet (a plastic reflection sheet), undergoing a micro-prism process on the surface of a thermoplastic resin sheet, has been employed in the reflection panel field, the fashion field, an architecture field and so on.
In the United States, the use of a glass bead type and a cube comer type are approved as the aforementioned reflective ability sheet. Commonly, the reflective ability sheet of the glass bead type is superior in short-distance visibility, and the reflective ability sheet of the cube comer type is superior for long-distance visibility and luminance created by optical reflection.
In the production of the reflective ability sheet of the cube corner type, an emboss pattern on an emboss pattern forming die (or a pattern embossing die) should be precisely transferred onto the thermoplastic resin sheet.
Therefore, it is especially important that the thermoplastic resin sheet is pressed onto the emboss pattern forming die (or the pattern embossing die) with appropriate pressure, and further, the pressure is continuously added for a predetermined period of time.
As conventional methods for producing the reflective ability sheet serving the above requirement, for example, a continuously pressing method (Japanese Patent Application Publication No. Sho60-56103), a belt method (Japanese Patent Application Publication No. Hei5-17023), and a roller method (an example relating to FIG. 9 in Japanese Patent Application Publication No. Hei3-4305 1) are proposed.
With the continuously pressing method, emboss pattern forming dies (or pattern embossing dies) are sequentially pressed onto a sheet material of solid phase, laid on a belt and continuously supplied with plural pressing means having a heating or cooling function to transfer patterns onto the sheet material.
With the belt method, a belt having an emboss pattern and a thermoplastic resin sheet are pressed between a pair of rollers to transfer patterns onto the sheet.
With the roller method, an emboss pattern is transferred onto a sheet by using a roller forming the emboss pattern on its outer circumferential face.
According to the aforementioned continuously pressing method, the production speed is slow and apparatus is complicated and large in size.
According to the belt method, the belt itself carries the emboss pattern, so that apparatus is large in size, and a disadvantage arises concerning the endurance of the belt as a pattern embossing die.
And, according to the roller method, the production speed is faster and the endurance is better. But, the temperature of the sheet is not effectively controlled to increase when the emboss pattern is transferred onto the sheet and decreased when the sheet after being embossed is peeled from the roller, resulting in disadvantages concerning the pattern reproducibility and the peeling properties. In other words, the apparatus is not structured to have a large difference in temperature between an area of the roller where the pattern is transferred, and an area of the roller where the sheet is peeled, thus not allowing the precise pattern reproducibility and the smoothly peeling properties to be obtained.
And further, the reflective ability sheets obtained by the conventional producing methods are not satisfied in regard to the reflecting properties.